Electrical regulating system



July 27, 1948. I R. R. LOBOSCO ELECTRICAL REGULATING SYSTEM 3Sheets-Sheet 1 Filed Aug. 25, 1944 INVENTOR ROSCOE R. LOBOSCO ATTORNEYJuly 27, 1948. R; R. LOBOSCO 2,445,789

ELECTRICAL REGULATING SYSTEM Filed Aug 23, 1944 A.C. 3-2 96:) 5 TPHINVENTOR ATTORNEY 3 Sheets-Sheet 2 oscoe mososco July 27, 1948. R. R.LoBosco I ELECTRICAL REGULATING SYSTEM Filed Aug. 23, 1944 'INVENTORROSCOE R. LOBOSCO wugow LIJ ATTORNEY Patented July 27, 1948 UNITED smas-PATENT OFFICE mem s. ii mmesrsm I .Roscoe R. Lobolco, Elizabeth, N.J.,asalgnor to The Linde Air Products tionof Ohio Company, a corpora-Application 1mm 23,1944, 8erial No.. 550,131"

s This invention relates electrical regulating systems, and moreparticularly to electronic circuits adapted to maintain a variablecharacteristic ata substantially constant preselected valuewhichisadlustable.

In many electrical regulating systems there is need. for apparatus whichcontrols energization of electrical circuits in accordance with apredetermined controlling influence, such asan electrical characteristicor an associated circuit or apparatus, to accomplish a desiredcontrolling function. There exists, for example, a demand formotor'control systems by which the speed mand for voltage regulatingsystems in which the magnitudes of currents in control circuits arecontrolled in accordance with the voltage of an associated circuit orapparatus to eflect the desired controllingor regulating operation. Anumber of electronic motor control clrcuits or units are now available.Some of such units have excellent characteristics with motors the'ratingof which is one horsepower or larger, but rather poor characteristicswith smaller motors, unless the motor is designed especially for thepurpose. However, none of such units is entirely suitable.

for use with motors of the series type.

There is also a great demand for Inv gas cutting and welding machines,small fractional horsepower motors are generally used to drive theblowpipe carriage. Such motors have ample torque to take care or anyblowpipe carr-i-age driving requirements, since the load issubstanrtially constant'and relatively small. Highspeed series motorshave characteristics which render them particularly suitable for drivinggas cutting machines. Such motors, for example, have an excellent torquecharacteristic; they are light in weight and compact; can be obtainedwith attached speed reduction at reasonable cost; and have proven to bevery reliable and trouble free.

However, fractional-horsepower motor speed control circuits nowavailable are not entirely suitable rorprecise adjustable speed controlthrough a wide range of speeds.

It is, therefore, among the objects of this invention to provide areliable, wide range, motor speed conrtrol system that is suitable forfractional-horsepower high-speed motors, particularly those ofthe'series type. However, the invention is not limited to the speedcontrol oi a fractional horsepower-series motor. but is applicable tothe control of both series and shunt motors of both fractional andintegral horsepower ratings. f

The speed control of series motors by electronic control circuits isdimcult, because the speedload characteristic 0! series motors is verypoor and changes of as much as 200% in applied voltage are sometimesnecessary to correct for large changes in load. Another object of thisinvention, therefore, is to provide an electronic control circuit havingan unusually wide motor-speed adjustment range, which is capable ormaintaining at any desired value the speed of a series or shunt motorregardless of wide changes in load and in line voltage, and which willremain in calibration for a relatively long time.

derived i'rom an alternating current supply circuitis applied to theanode circuit of the tube, while an alternating voltage also derivedfrom such supply circuit is applied to the grid circuit in such mannerthat the grid voltage lags the anode voltage, causing the tube to the byvirtue of the phase relationship or such alternating voltages. Arectifier is connected to the supply circuit so as to energize anadjustable voltage divider or potentiometer having a direct currentoutput circuit connected so as to superimpose a unldireotionalgridbiasing voltage on the alternating voltage applied .to the grid circuit.Means responsive to the operation of the motor is arranged to supplydirect current at a variable unidirectional voltage which variesaccording to a characteristic, such as the speed of the motor, the valueof which is to be regulated, and a circuit is connected so as tosuperlmpose such variable unidirectional voltage on the alternatingvoltage applied to the'grid circuit, in potential opposition to theunidirectional grid biasing. voltage of the voltage divider outputcircuit. The

circuit arrangement is such that the motor is aument of the invention asapplied to a motor speed control system;

F 2 is a view mainly in side elevation and partly in section of themotor and a. two-phase generator; T

Fig. 3 is a view in cross-section taken on line 3-3 of Fig. 2;

Fig. 4 is a circuit diagram of a modification of the invention asapplied to the speed-control of a shunt motor; and

Fig. 5 illustrates an embodiment of the invention as applied to anelectrode feed-control system for arc welding.

Referring to Fig. 1 of the drawing, the illustrated electronic controlcircuit includes a universal type A. C.-D. C. series motor M having anarmature A and a field, winding F. The motor M is connected to thecommon output circuit of a pair of suitable gaseous tubes such asthyratrons Ti and T2 by conductors II and i2, connections KI,K2, K3 andK4, and a reversing switch l3. The motor M drives an alternating currentgenerator G, the entire control system being energized by an alternatingcurrent supply circuit ll. A control circuit i6 is connected to thesupply circuit H by a switch i5, and safety fuses FI and F2 are providedin the power supply conductors. A pilot light PL is connected acrosssuch conductors to indicate when the circuit i6 is energized. Connectedto the circuit iii are the primary windings PI, P2 and P3 oftransformers TRI, TR2, and TR3. The primary winding P3 is connected tothe circuit Hi by a normally open switch TP of a time delay relay TDwhich is connected across such circuit. Upon closing the switch IS, thetime delay relay TD is adapted to close the switch TP after a suitabletime interval permitting the cathode heaters l8 of thyratrons TI and T2to become hot, such heaters being connected to the secondary winding S2of transformer TR2 by conductors X, X. Thus, transformer TR2 suppliesthe cathode heating power for the thyratrons Ti and T2.

Transformer TR3 supplies the motor power through the tubes TI and T2.The anodes 20 of ,the thyratrons TI and T2 are connected to oppositeterminals 2l of the secondary winding S3 of the transformer TR3, themid-point of such winding being connected to the conductor II .whichleads to the motor field winding F through a safety fuse F3. Thecathodes 22 of thyratrons TI and T2 are connected by a common circuit 23to the conductor i2 leading to the motor armature A through thereversing switch l3, the connection 24 between circuit 23 and conductori 2 being grounded at Gr. 7

A rectifier tube T3 is employed as a conventional full wave rectifier tosupply power to the field SF of a shunt wound motor Sm, if such a motoris used, through connections K5 and K6. When the series motor M is used,however, the connections K5 and K6 are, of course, unnecessary.

The transformer TR3 is provided with a pair of secondary windings SEhaving connections A, B and C with a resistor RFS and a condenser CFS,forming a phaseshift network which supplies to the control grids 23, 26of the thyratrons TI and T2, through a. transformer 'IRA, an alt hatingvoltage which lags the alternating voltage applied to the anodes 20, 20of these tubes by a phase angle of the order of The secondary winding 84of the transformer TR is connected at its opposite terminals to thecontrol grids 26 through suitable resistances 23, 23, and to thecathodes 22 through condensers 30, 30.

The center tap ll of the secondary winding S4 of transformer TR4 servesas a convenient means of superimposing on the alternating voltage,applied tov the grids 23, a unidirectional grid biasing voltage in orderto cause the output current of the thyratrons TI and T2 to be increasedor decreased in accordance with whether such unidirectional voltage ispositive or negative.

The transformer TRI supplies power to a potentiometer or voltage dividerPl through the full wave rectifier tube T3, the output circuit of whichincludes filter elements comprising a resistor RI and condensers Cl Clwhich act with a condenser C2 to smooth the pulsating direct currentoutput of the rectifier tube T3. A gaseous-discharge type of voltagecontrol tube TI is connected across the output circuit of the rectifiertube T3 for the purpose of maintaining the unidirectional voltage acrossthe voltage divider Pl constant regardless of voltage changes in thealternating current supply circuit it, making the speed of the motor Mconstant regardless of line voltage variations or condition of therectifier tube T3.

The alternating current generator G, which is driven by the motor Mthrough shaft 34, preferably comprises field coils GI and G2 having atwo-phase output voltage which is proportional to the speed of themotor. The output current of the coils GI and G2 is fed to voltagestep-up transformers TR! and TRI. The secondary current of suchtransformers is rectified full wave rectifier tubes T3 and T1 andenergizes a resistor B2. A condenser C3 is connected across the resistorR2 to smooth the rectified generator voltage which is applied to suchresistor R2. The negative terminal of the resistor R2 is connected tothe center tap 3| of the transformer winding S4 by a conductor 33containing a source of negative bias voltage, such as a C" batteryCB.

The generator G is of the two-phase type because the rectified voltageoutput thereof has a much smaller percentage of ripple than that of asingle-phase generator and rectifier, less ripple is present in theformer than in the latter. Smootheroperation and lower motor speeds areobtained with a two-phase generator than with asingle-phase generator.However, a single-phase generator may be used if desired.

Referring particularly to Figs. 2 and 3, there is illustrated a suitabletwo-phase generator G comprising an armature consisting of a 4-polemagnet 32 mounted on the shaft 34 of motor M. The generator field coilsGI and G2 are adjustably mounted on a bracket 33 by flexible arms 31,the gap between the four-pole magnet 32 of the generator coils GI and G2'being changed by means including levers 35 and long fillister-headscrews 33, 33. The gaps between the armature and field coils areadjusted so that the output voltage of each of the two cells is equal toa desired value. The governor parts are simple to make and have verywide tolerances since the gap adjustment feature takes care of anymanufacturing variations in the parts. The generator is provided with asuitable housing 39 supported by the frame of the motor M.

In addition to low cost and simplicity the alternating current generatoror tachometer G and rectifier TI, TI

5 have other advantages. Where an alternating current tachometer orgenerator and rectifier are used. according to the invention. thetachometer leads AT need not be reversed when the motor M is reversed.When. a dirct current tachometer or generator is used it is necessary toreverse both the motor and the tachometer leads. Since in this lattercase both control leads and power leads are involved, the reversing oithe motor is much more complicated. An examination of the circuitillustrated by Fig. 1 will show that the sum of the rectified generatorvoltage appearing across the-resistor R2. and the speed control voltageappearing across the output terminals 40 and 4-2 of the volt;

age divider PI, is superimposed on the negative bias voltage and thealternating voltage appearing on the control grids II of the thyratronsTl Y across terminals II and 2' of the voltage divider to test theoperation of the tubeTl.

Pl to indicate the speed control voltagethat' is applied to the inputcircuit of the thyratrons Ti, and T2. Also a voltmeter may be connectedby conductors U1 across the shunt field winding SF The meter TM itselfmay be'located in any desired position. If desired, the meter may beprovided in a unit U with a multipoint switch M8, so that it may beconnected at will to any desired part of the system for testing variousparts of the system. for example, the operation of the generator ,coilcircuit AT, the generator rectifier circuit ET, the

, speed adjustment circuit C1, the thyratrontubes,

the motor field supply circuit DT, and as atachometer, the meter TMbeing suitably calibrated and T2. A further examination of the circuitwill show that the polarity of the speed control voltage is such thatitapplies a positive unidirectional voltage on the grids of thethyratrons, while the polarity of the rectified generator voltage issuch that it applies a negative unidirectional voltage on the grids ofthe thyratrons.

' The actual uhidirectional voltage superimposed on the grids 26, is thealgebraic sum of such two voltages and that of the 0" battery CB.

Thus, when the switches I 3 and llare closed to start themotor M, thegenerated voltage will be zero and there will be a high positiveunidirectional voltage superimposed on the alternating voltage of thegrids of the thyratrons, which in eii'ect causes the phase of thealternating volt age applied to the grids to shift so that maximumcurrent flows through the field F and armature A of the motor M. Suchpositive voltage is bucked by the negative bias voltage of battery CB,so that the motor will operate at a relatively low minimum speed. As themotor armature A comes up to the preselected speed the rectifiedgenerator voltage appearing across the resistor R2 increases untii'itapproaches the value of the speed control voltage across the terminals40 and 42 offthe voltage divider Pl, causing the phase ofthe gridvoltage gradually to shift and finallystabilize at a value whichdelivers to the motor M such power that the rectified generator voltageis substantially equal to the speed control voltage. Any tendency forthe motor armature A to shift in speed causes .achange in the generatedvoltage which. in turn, causes the grid phase to shift in such directionthat the change in current to the motor, caused by this phase shiftbrings the motor back to the selected speed. The speed of the motor maybe adjusted to any predetermined value through a relatively wide rangeby adjusting the position of the positive terminal 40 of the voltagedivider Pl. For some applications and under certain conditions a circuitusing a single thyratron is satisfactory. I

The speed of the motor armature A may be indicated by a meter-typetachometer TM, which can be connected to the circuit in any oneofseveral places for example, a voltmeter, calibrated in any, suitablemanner to indicate the speed of the motor or a member, such as theblowpipe for such indications. Thus, the entire circuit.

can be checked quickly by moving single switch MS to each of severalpositions in quick succession and noting the meter readings. Thus, any

trouble may be located'without' the use of complicated test equipmentand without any knowledge of the system by the person doing the testing,by merely following a few simple instructions.

The speed, control potentiometer or voltage dividertPi can be located inany desired position and, if necessaryor desirable, a plurality ofvoltage dividers or potentiometers may be connected into the circuit tooperate as desired. Since such. units are lnexpensiveand require only asmall three-wire lead, several of them may be located at convenientpoints about the machine.

without appreciably increasing the cost 01' the 7 system. The electronicpower control device comprising one or two thyratrons'may also be I Ilocated wherever desired. Thus, the four major units of the presentsystem, i. e. the speed adjustment means PI, the tachometer TM, themotor M, and the electronic device Ti, can be placed in any desiredlocation with respect. to one another without interfering with theoperation of the system.

The circuit shown in Fig. 1 may be varied or simplified in a number ofways, for example:

1. A single generator coil and a single rectifier tube can besubstituted for the two-phase generator and two rectifier tubes withsome sacrifice in performance at low motor speeds.

2. A direct current tachometer generator can be connected directlyacross the resistor R2, in which case the two-phase'generator system,the

two associated transformers and the two rectifier tubes may be omitted.1 I i 3. When the back electromotive force of ashunt wound motor is usedin place of a genera ator, the two step-up transformers TRG and TRT Iand two rectifier tubes T6 and T1 are'omitted.

4. Instead of two thyratrons operating as a full wave rectifier, asingle thyratron operating as a half-wave rectifier may be used.

I 5. The voltage control tube T4 in the speed control'circuit can beeliminated provided linevoltage variations do not cause any .troubldriven thereby, may be connected by conductors By taking i'ull'advantageof the forego ng simplifications, it is possibleto obtain good-performance with a simplified circuit using only two tubes for a shunt motorand onlythree tubes for a series motor. s

A shunt motor with fixed field excitation Igencrates a backelectromotive force thatis proportional to the speed of the motor.Therefore, it is possible to make use of such electromotive force tocontrolthespeed of the motor. Fig. 4 shows how this may be accomplishedaccording to the present invention.. In such system, in which the linevoltage variations.

corresponding parts have the same reference characters as Fig. 1, asingle thyratron Tl supplies half-wave current to the shunt motorarmature A. the shunt field F of the motor being connected across theoutput circuit of the rectifier T3, the

' back electromotive force of the armature opposes v,the voltage of thepotentiometer Pl.

with Fig. 1 except that the generator G is dispensed with, and the backelectromotive force generated by the motor armature winding A isemployed to match the unidirectional voltage output of the voltagedivider Pi. This circuit has been found to give unusually goodperformance.

With a series motor circuit, according to the invention, the generatedvoltage is proportional to the speed of the motor regardless of linevoltage variations. However, were it not for the voltage control tube T4the speed control voltage would vary with line voltage variations andthus cause the motor speed to change with line voltage variations.Therefore, the use of the voltage regulator tube to maintain the speedcontrol voltage at the adjusted value, according to the invention, makesthe speed of the series motor substantially independent of line voltagevariations.

With a shunt motor circuit the motor counter electromotive force willvary it the motor field strength varies. Therefore, the field shduid bemaintained well saturated so that normal line voltage variations willnot affect such counter electromotive force. The combination of a wellsaturated field and the voltage regulator tube T4, according to theinvention, makes the speed of the shunt motor substantially independentof Since the motor speed'is substantially independent of motor load andline voltage, and since themotor speed is a function of the speedcontrol voltage, a suitably calibrated voltmeter TM connected acrosscircuit CT, Fig. 1, so as to be responsive to the speed control voltageapplied to the grid of the thyratron, provides an accurate indication ofthe motor speed or a characteristic which is proportional to such speed.

Figs. 1 through 4 illustrate how the speed of a shunt or series motor ismaintained constant at any desired value regardless of load or linevoltage changes by making use of a generated voltage that isproportional to the speed of the motor. However, the principles of theinvention may be usedin a rod or electrode feed control system for arcwelding by connecting the arc circuit in place of the generator coilsand reversing the potential of the rectified voltage and the "speedcontrol voltage. The voltage divider is then adjusted to the desired arcvoltage, and the rod feed motor will adjust itself to maintain the workvoltage at that value. Fig. 5 illustrates a system for accomplishingthis result. In a similar manner the output of a photocell, anemplifier, or any other device which will deliver a tic constant. Theinvention can also be used to control the speed of a shaft receiving itstorque a from a motor by using the system to control a magnetic couplingbetween the motor and the shaft.

Referring to Fig. 5, the primary winding P! of a transformer TR5 isconnected across an arc welding circuit AW including a welding rod orelectrode EL and a work-piece WP. The electrode is fed toward thework-piece by a shunt motor having an armature A and a field wind ing F.The armature A is included in the output circuit Ii, l2 of thethyratrons TI and T2. The switch TP is closed by the time delay relayTD, energizing the primary winding P8 of transformer T33.

The dual secondary winding 88 of the latter energizes the output circuitll, l2 of the thyratrons TI and T2 and the motor armature with rectifiedcurrent the value of which is controlled by the voltage applied to thethyratron control grids 26. Alternating voltage is applied to the grids26 by transformer TR, the opposite ter-' minals of the secondary winding8 being connected to the grids through resistors 28. The phase of thealternating voltage applied to the grids 26 is caused to lag that of thealternating grid voltage by an angle of the order of 90, by a.phase-shifter circuit including a resistor RFS and a capacitor CFS inthe circuits A and C, respectively, which connect to opposite terminalsof the transformer secondary windings SE. One terminal of the primarywinding P4, cdnnects to the common terminal CT of the secondary windings SE, the other being connected to the common connection of RFS andCFS. The cathode heaters iii of the tubes TI and T2 are energized by thesecondary winding S2 of transformer TR. through conductors X, X.

The motor field F winding is energized with rectified current from thefull-wave rectifier tube T3 which is in turn supplied with alternatingcurrent by the transformer TRI having primary winding PI and secondarywinding SD. The cathode 52 of the tube T3 is energized by secondarywinding SI, the mid-terminal 64 of the latter being connected byconductor 56 to one terminal oi the motor field windin F, which is agrounded at Gr, and the mid-terminal 56 of the winding SD beingconnected by conductor 60 to the other terminal of the field winding.Voltage divider P is connected acrossthe motor field is also connectedacross such winding to smooth out current ripples. The adjustable tap 40of the voltage divider P is connected to resistor R2 by conductor 82.Such tap may be provided with a scale calibrated in welding-arc voltageunits. N7

The resistor R2 is also connected by conductors 64 and 65 to the directcurrent output circuit of rectifier tubes T8 and T9 which are energizedby the secondary winding S5 of transformer TR5. The output circuit ofthe tubes T6 and T9 includes a load resistor 66 and 9. cur

rent smoothing condenser 61. Thus, the uni- -directional voltage appliedto the terminals '8 voltage which is proportional to some desired acharacteristic, can be connected to the resistor R2, to cause the motorspeed to vary in such manner as to keep the value of such characterisand I6 01' the resistor R2 by the conductors II the circuit 22 includingthe source CB of bias voltage to the mid-top 3| of the secondary winding84 of transformer 'I'RA. This bias voltage increases the range ofarc-welding potential ad- Justment of the rod-feed motor, by decreasingthe minimum speed of the motor;

In the operation of thasystem shown in Fig. 5, the power supplied to.the rod-feed motor armature A by the thyratrons TI and T2 isautomatically varied so as to keep the arc-welding voltage constant. Thevalue of the latter is 'determined by the adjustment of the tap to ofthe voltage divider P. The unidirectional voltage applied to the grids26 by virtue of resistor R2 from the arc voltage rectifier tubes T8 andT9 tends to increase the rod-feed, which decreases the unidirectionalvoltage applied to the grids 28 by virtue of resistor R2 from the outputcircuit of the rectifier tubes T8 and T9. Thus, the arc-welding voltageis kept constant, any incremental change in the latter being met by acompensatory change in the operation of the motor;

, Let it be assumed that the unit is ready to operate and that an archas been struck. The rectifier tubes T8 and T9 supply to the grids of 10connecting said voltage divider to a source of direct current, saidvoltage divider having a direct current output circuit connected so asto superimpose a unidirectional negative voltage on the alternatingvoltage applied to said grid circuit;

a resistor, means including a welding circuit the voltage of which isresponsive to the speed of said motor for supplying direct current tosaid resister so that the unidirectional voltage across ent upon theadjustment of said voltage divider.

tubes TI and T2 a positive voltage proportional to the arc voltage.Therefore, the actual D. C. potential on the grids of the tubes TI andT2 will be the algebraic sum of the negative bias voltage supplied bythe voltage divider P and the positive voltage supplied by the arcvoltage rectifiers T8 and T9. In normal operation thesetwo voltages arenearly equal. If the arc voltage is greater than the desired value, thenthe algebraic sum of these two voltages will tend to'make the'grid morepositive which will cause the phase of the and voltage to shift so as toincrease the motor current which will in turn reduce the arc gap andtherefore, the arc voltage; Similarly if the arc voltage is less than isdesired the algebraic sum of these voltages will tend to make the gridsmore negative and thus shift the phase of the grid voltage so as toreduce the motor current and therefore the motor speed thus causing thearc gap and the arc voltage to increase.

I claim:

a 1. An electrical regulating system for smoothly controlling the rateof rod feed in'a welding ma chine including a direct current rod-feedmotor, such system comprising the combination of at least one thyratron,means for supplying an alternating voltage to the input circuit of saidthyra tron, means for passing the rectified current output of thethyratron through the armature of the rod-feed motor, and means forselectively regulating the welding voltage -includin'g means forapplying to the grid of said thyratron, an alternating voltage laggingthe platevoltage of the thyratron by approximately 90 degrees, aunidirectional positive voltage proportional to the actual weldingvoltage, and a unidirectional nega ative voltage proportional to thedesired welding voltage.

2. In combination, at least one grid-controlled gaseous-discharge tubehaving a grid circuit and an anode circuit, a welding rod feed motorassociated with said tube scrthat ithe d of said motor is controlledthereby, means for applying an alternating voltage derived from analternating current supply circuit to the anode circuit of said tube,means for applying an alternating voltage derived from said supplycircuit ,to the grid circuit of said tube whiclngrid voltage lags theanode voltage by a fixed angle of approximately 90 degrees. anadjustable voltage divider, means 3. An electrical regulating system formaintaining substantially constant the speed of a direct current motor,which speed is adjustable,

comprising the combination of an electronic speed control circuit of thetype in which a voltage responsive to the actual motor speed is matchedby a reference voltage which is adjustable to set the motor speed to adesired value, and the difference between such voltages maintains suchspeed constant at the desired value, and a voltmeter connected to suchcircuit sosas to be responsive to such reference voltage, and calibratedto indicate a function of the motor speed, so that the desired value ofsuch function can be preset by.

adjusting such reference voltage to correspond to the'value of thefunction indicated by said voltmeter before the motor isstarted.

-4. An electrical regulating system for maintaining substantiallyconstant the speed of a direct current motor, comprising the combinationof means for supplying an alternating voltage to the input circuit of athyratron, means for passing the rectified current output of thethyratron through the armature of the said motor, and

means for selecting the desired speed at which the motor will operate,including means for applying to the grid of the thyratron a'unidirectionalnegative voltage proportional to the actual speed of themotor, an alternating voltage of fixed value lagging the plate voltageby approximately 90 degrees, a negative unidirectional voltage of fixedvalue which determines the minimum speed of the motor, and aunidirectional positive voltage proportional to thedesired speed of themotor, and a voltmeter connected to measure such a unidirectionalpositive voltage, and thus indicate the selected motor speed before, andafter, as well as during the running of the motor.

ROSCO E R; LOBOSCO,

I asrnnnivcns crrnn The following'references are of record in the fileof this patent:

UNITED STATES PATENTS

